Zeolites are crystalline aluminosilicate molecular sieves which have a microporous three-dimensional framework structure. In general, the crystalline zeolites are formed from corner-sharing AlO.sub.2 and SiO.sub.2 tetrahedra and are characterized by having pore openings of uniform dimensions, having a significant ion-exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal, without significantly displacing any atoms which make up the permanent crystal structure.
Zeolite beta, which is described in U.S. Pat. No. RE 28,341 and is incorporated by reference, is one particular zeolite which has recently received considerable attention for catalyzing various types of reactions. Zeolite beta is usually synthesized in a basic medium in the presence of tetraethylammonium and alkali cations and has a Si/Al mole ratio from about 5 to about 100. A molecular sieve with the zeolite beta structure but containing titanium in the framework is described in Spanish patent no. 2,037,596 which also discloses that the titanium containing material can be used as a catalyst in selective oxidation reactions of organic compounds using hydrogen peroxide, organic peroxides or hydroperoxides as the oxidizing agent.
WO97/33830 discloses the synthesis of zeolite beta using fluoride anions as the mineralizing agent at or near neutral pH. It is disclosed that these materials exhibit enhanced thermal stability and low concentration of SiO or SiOH defects over a wide chemical composition range. Finally, T. Blasco et al. in J. Phys. Chem. B, 1998, 102, p. 75 disclose the incorporation of titanium into the beta structure by using the procedure in WO97/33830 again over a wide Si/Al range. These materials also have increased hydrophobicity.
In contrast to this, applicants have synthesized a series of molecular sieves comprised of at least SnO.sub.2 and SiO.sub.2 tetrahedral units. Titanium and germanium can also be present in the framework. These molecular sieves are represented by the empirical formula: EQU (Sn.sub.x Ti.sub.y Si.sub.1-x-y-z Ge.sub.z)O.sub.2
where "x", "y" and "z" are the mole fractions of tin, titanium and germanium. These stannosilicate molecular sieves are useful as catalysts in selective oxidation processes such as olefin epoxidation and hydroxylation of aromatic compounds.